464 Charles R. Stockard 



Adami ('01) has also presented the general importance of this 

 point of view, designating the tumor process as the cumulative 

 "habit of growth replacing the habit of work. " 



Considering both these statements and Morgan's, one may 

 express the case as follows. Undifferentiated tissue is that which 

 has not begun to function and so employs all of its energies in 

 growth. When a limb is removed the tissue at its base can no 

 longer function so that it gives up its differentiation and begins 

 to grow again. I agree with Morgan when he states that "because 

 a tissue had become differentiated it has not lost the potentiality 

 of becoming young again, provided it gives up its differentiation." 

 However, neither Morgan nor Emmel have drawn any similarity 

 between the action of regenerating tissues and malignant growths. 

 The one difference I wish to point out, however, between regen- 

 erative growths and tumor growths is that the former sooner or 

 later stop on account of differentiation and function having begun 

 while the latter are not inhibited by such forces and so continue 

 to grow indefinitely. 



I believe that additional evidence in support of the above views 

 is furnished by the medusa and perhaps also by the brittle-star. 



The medusae in all cases were unfed and decreased steadily 

 in size during the experiment. The decrease in size was without 

 exception greater in those specimens which were regenerating a 

 larger number of arms when compared with others regenerating 

 fewer. In passing through the series each group was smaller 

 than the preceding groups regenerating fewer oral-arms but always 

 larger than the following groups which were regenerating a greater 

 number of arms. The series is illustrated in plate I, a photo- 

 graph of six medusae each regenerating successively greater num- 

 bers of parts. The specimens were all equal in size at the begin- 

 ning of the experiment but are now successively smaller as the 

 number of regenerating parts is increased. 



It may be argued that the greater removal of tissue lowers the 

 possible food supply to be drawn on by other parts. It is equally 

 true, however, that when more parts are removed fewer remain to 

 require nourishment from any source. 



The oral arms which are supplied with nematocysts normally 



